Multiple coat metal pipe and its fabrication method

ABSTRACT

To provide a multiple coat metal pipe and its fabrication method having excellent corrosion resistance without deteriorating chipping resistance or splashing resistance, capable of being fabricated easily and capable of simply carrying out peel off operation owing to a weak peel off strength wherein corrosion resistance of an end working portion is not deteriorated, there is provided a multiple coat metal pipe which is a metal pipe constituted by multiplexing and coating a first layer including a resin having an adhesive force in respect of a surface treatment layer formed on an outer peripheral face of the metal pipe and capable of being extruded and a second layer provided on an outer peripheral face of the first layer, having a chipping resistance and capable of being extruded, wherein a peel off strength between the first layer and the second layer is 75 g/cm or less.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multiple coat metal pipe and itsfabrication method in which in a metal pipe comprising a comparativelyslender diameter of a pipe diameter of 20 mm or smaller which isarranged particularly at a lower portion of a chassis as a pipe of abrake pipe, a fuel pipe or the like in an automobile or the like,multiple coat layers are provided on its outer peripheral face forachieving durability against chipping (flying stone) or splashing (muddywater) in running and end working of flaring, spooling and buldging orthe like is carried at a pipe end portion thereof in later steps.

2. Description of the Prior Arts

In recent years, there have been proposed a number of resin coat metalpipes for pipes of brake pipes, fuel pipes and the like arranged at alower portion of an automobile in which coating layers are formed in athick film shape to provide chipping resistance or splashing resistance.

As such a coated metal pipe, there have been known a metal pipe formedwith a chromate coating as necessary on a Zn (zinc) or Zn/Ni (nickel)plated film that is coated on an outer peripheral face thereof, furthercoated with polyvinyl fluoride (PVF) having a thickness of about 20 μmand coated with a thermally contractive tube further thereon therebyforming multiple coat layers and a metal pipe formed withpolyamide-based resin (PA) such as PA 11 or PA 12 having a thickness ofabout 200 through 300 μm by extrusion on a Zn or Zn/Al (aluminum) filmthat is coated on an outer peripheral face thereof.

However, according to the former conventional technology, there poses aproblem in which a product cost is increased since the expensivethermally contractive tube is used and time and labor are needed infabrication since the technology includes a step of heating forcontracting the tube after the thermally contractive tube is covered onthe polyvinyl fluoride layer which deteriorates the productively andaccording to the latter conventional technology, there poses a problemin which the corrosion resistance is deteriorated when the pipeundergoes attack of chipping or the like since a single layer ofpolyamide-based resin in a thick film shape is used.

Hence, as a result of studying in various ways in respect of a coatedmetal pipe having excellent corrosion resistance without deterioratingchipping resistance or splashing resistance and facilitating thefabrication, the inventors have paid attention to a metal pipe havingmultiple coat layers in which on an outer peripheral face of the metalpipe previously subjected to a surface treatment, a resin layercomprising a polyamide-based resin (PA), polypropylene (PP),polyethylene (PE), polyvinylidene fluoride (PVdF) or the like havingadhesion force in respect of the surface treatment layer, is formed asan inner layer, on which PP, PE or polyamide-based resin similar to theabove-described having chipping resistance or splashing resistance, iscoated over an entire length. Further, in respect of a multiple coatmetal pipe constituted as described above, a soft chipping test usingstones having a size of 2.5 through 5 mm with an amount of flying stonesof 500 g×1 time under air pressure of 1 kgf/cm² and a hard chipping testusing stones having a size of 5 through 9 mm with an amount of flyingstones of 500 g×5 times under air pressure of 5 kgf/cm², have beencarried out and a result in respect of the chipping resistance has beenobtained as expected by the inventors.

According to the multiple coat metal pipe constituted as describedabove, a satisfactory result has been obtained in respect of thecorrosion resistance without deteriorating the chipping resistance orthe splashing resistance as mentioned above, the following problem isposed when the pipe is actually arranged at the lower portion of anautomobile or the like. That is, normally, end working of flaring,spooling, buldging or the like is carried out to mutually connectmultiple coat metal pipes and in that case, an outermost layer of themultiple coat layers of the metal pipe is peeled off and thereafter, theend working is carried out. However, in the case of the above-describedmultiple coat metal pipe, in peeling off the outermost layer, there havebeen cases in which the inner layer adheres to the outermost layer andis peeled off along therewith or although the inner layer does notadhere to the outermost layer, the inner layer is partially peeled offfrom the coated film.

When the inner layer is also peeled off in this way, the corrosionresistance of the end working portion is deteriorated and therefore, incarrying out the peeling off operation, in order to prevent occurrenceof the situation where the inner layer is peeled off, close attentionmust be paid and therefore, time and labor is needed in the operation,the operational performance is significantly deteriorated and theproductivity cannot be improved.

SUMMARY OF THE INVENTION

The present invention has resolved such a problem and it is an object ofthe present invention to provide a multiple coat metal pipe and itsfabrication method having excellent corrosion resistance withoutdeteriorating chipping resistance or splashing resistance, capable ofbeing fabricated easily and capable of simply carrying out peel offoperation owing to a weak peel off strength wherein corrosion resistanceof an end working portion is not deteriorated.

In order to achieve the above-described object, the inventors havecarried out various researches and completed the present invention tofind out that in extruding two layers of resin layers on an outerperipheral face of a metal pipe on the outer peripheral face of which asurface treatment has been carried out by an electric or molten platingprocess or the like, by bringing the both layers substantially into anon-adhesive state such that a peel off strength between the both layersis 75 g/cm or less, excellent corrosion resistance is achieved withoutdeteriorating chipping resistance or splashing resistance, the peel offoperation can easily be carried out and corrosion resistance at an endworking portion is not deteriorated.

Therefore, according to a first aspect of the present invention, thereis provided a multiple coat metal pipe which is a metal pipe constitutedby multiplexing and coating a first layer comprising a resin having anadhesive force in respect of a surface treatment layer formed on anouter peripheral face of the metal pipe and capable of being extrudedand a second layer provided on an outer peripheral face of the firstlayer, having a chipping resistance and capable of being extruded,wherein a peel off strength between the first layer and the second layeris 75 g/cm or less.

Further, according to a second aspect of the present invention, there isprovided a method of fabricating a multiple coat metal pipe, wherein afirst layer comprising a resin having an adhesive force is extruded on asurface treatment layer provided on an outer peripheral face of a metalpipe and a second layer comprising a resin having a chipping resistanceis extruded on an outer peripheral face of the first layer and the bothresin layers are brought into contact with each other and aremultiplexed with each other substantially in a non-adhesive state. Inthis case, it is preferable that when the resins of the first layer andthe second layer are provided with mutual dissolving performance, thesecond layer is extruded at a temperature equal to or lower than themelting point of the first layer and when the resins of the first layerand the second layer are not provided with the mutual dissolvingperformance, the second layer is extruded at a temperature equal to orhigher than the melting point of the first layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a), 1(b), 1(c) and 1(d) are perspective views showing an outlineof a peel off test used in the present invention in which FIGS. 1 (a),1(b), 1(c) and 1(d) are views showing its procedure; and

FIG. 2 is a sectional view showing an embodiment of an extrusion coatingdevice used in fabricating a multiple coat metal pipe according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

First, a metal pipe used in the present invention is a seamless pipe, asemi-seamless pipe, an electrically welded pipe or a metal pipecomprising a soldered pipe or a welded pipe having previously a coatedfilm of a copper alloy and fabricated by being wound in a single layeror multiple layers, which is provided with an outer diameter of about 20mm or smaller. Further, its outer peripheral face is subjected to asurface treatment of a plated film of zn, Al or alloys based thereonthrough the electric plating process or the molten plating process andcoated with a film of chromate such as yellow chromate, olive chromateor the like on the surface of the plated film or the like as necessary.

Further, the surface treatment layer may be coated with a single layerof epoxy-based resin, polyamide-based resin, silane coupling agent,titanium coupling agent or the like as a primer by means of extrusionforming, spraying, showering, dipping, brush coating, powder coating,hot melting or the like.

Next, a first layer comprising polyamide-based resin (PA) of PA 6, PA11, PA 12 or the like is formed on the surface treatment layer or theprimer layer by a film thickness of 20 through 50 μm through extrusionforming. When the film thickness of the first layer is less than 20 μm,the corrosion resistance is deficient and meanwhile, when it exceeds 50μm, a fastening nut which has conventionally been used and prescribedcannot be used.

Further, a resin having chipping resistance, for example, polypropylene(PP), polyethylene (PE) or polyamide-based resin (PA) mentioned above iscoated on and multiplexed with the first layer over an entire length bya film thickness of 100 μm through 1.5 mm through the extrusion formingby which a second layer is formed. In this case, when the first layerresin and the second layer resin are provided with mutual dissolvingperformance, it is important that temperature of molten resin flowingout from a die main body of an extrusion coating device such that bothlayers of the outer surface of the first layer and the inner surface ofthe second layer are brought into contact with each other, is measuredby a sensor such as a thermistor or a thermocouple or a radiationpyrometer and the second layer is extruded at a temperature which isequal to or lower than the melting point of the first layer therebymultiplexing and coating the both layers. Meanwhile, when the firstlayer resin and the second layer resin are not provided with the mutualdissolving performance, the second layer may be extruded on the firstlayer at a temperature which is equal to or higher than the meltingpoint of the first layer resin.

Incidentally, the melting points of resins exemplified above are wellknown, for example, that of PA 6 is 210 through 220° C., that of PA 11is 191 through 194° C., that of PA 12 is 160 through 209° C., that ofpolypropylene is 168 through 175° C. and that of polyethylene is 130through 137° C.

Further, even when a defect, for example, a pin hole or the like iscaused at the first layer, the defect is covered by the second layer bywhich the defect can be prevented from being made continuous from theinner face to the outer face and as a result, the corrosion resistancecan be promoted.

Further, the reason for limiting the layer thickness of the second layerto the above-described range is that when it is less than 100 μm,sufficient chipping resistance cannot be provided and in the meantime,even when it is the layer thickness exceeding 1.5 mm, not only nodifferentiation is produced in promoting the chipping resistance, thesplashing resistance and the corrosion resistance but also when bendingis carried out, crack or the like may be caused in the multiple coatlayer.

In respect of the multiple coat metal pipe provided in this way, thesecond layer is peeled off while having the first layer remain in orderto carry out end working of flaring, spooling, buldging or the like,when the peel off strength between the first layer and the second layerexceeds 75 g/cm, there have been cases where the first layer adheres tothe second layer to be peeled off and is peeled off along therewith orthe first layer is partially peeled off from the plated film by whichthe corrosion resistance of the end working portion is deteriorated.Accordingly, in order to maintain a substantially non-adhesive statebetween the first layer and the second layer, the peel off strengthbetween the first layer and the second layer needs to be 75 g/cm orlower. A method of measuring the peel off strength used in this casewill be explained in reference to FIGS. 1(a),1(b), 1(c) and 1(d).

Among the multiple coat layers coated on the outer peripheral face of ametal tube cut in a predetermined length as shown by FIG. 1(a), a pairof cuts in the longitudinal direction having a predetermined width areproduced only at the external layer (refer to FIG.1(b)), the portion ofthe external layer is peeled off and thereafter the peeled-off portionis folded back upwardly as shown by FIG. 1(c) and as shown by FIG. 1(d),the peel off test is carried out by pulling an end portion of thepeeled-off portion relative to a lower end portion of the multiple coatlayers in an allow mark direction at a pulling speed of 20 mm/minutesand a result of the test is measured in respect of the peel off strengthon whether the inner layer is adhered to the outer layer.

Further, although a conventional extrusion coating device can be used inthe multiple coat metal pipe and a device for carrying out thefabrication method according to the present invention, a device as shownby FIG. 2 is preferable in order to control temperatures of resinsforming the multiple coat layers. That is, in FIG. 2, notation (11₁)designates an extrusion die in an extrusion coating device provided toextrude the first layer (1), a feeding gap (13) communicating with aresin supply port (12′) is held between opposed inner peripheral facesby a die main body (11′) and a guide core (12), a nozzle port (11″) isconstituted by a front end portion on the side of the die main body(11′), at inside of the guide core (12) a metal pipe (P) is movedforwardly by a feed device using rolls (not illustrated), a constantamount of resin is supplied from the nozzle port (11″) and the firstlayer (1) is extruded on the outer peripheral face of the metal pipe.

Next, an extrusion die (11₂) having a constitution similar to that ofthe extrusion die (11₁) is installed at an interval in the axialdirection of the extrusion die (11₁) and the metal pipe (P), a constantamount of resin is supplied from the nozzle port (11″) and the secondlayer (2) is extruded on the outer peripheral face of the first layer(1) to multiplex therewith and coat thereon.

Further, according to the present invention, a sensor such as athermistor or a thermocouple or a radiation pyrometer is installed ateach of a vicinity of the nozzle port (11″) of the extrusion die (11₁)and a vicinity of the nozzle port (11″) of the extrusion die (11₂) bywhich temperatures of molten resins flowing out from the nozzle ports(11″) are measured, the forming operation is performed such that atemperature of extruding the resin forming the second layer (2) ispreferably equal to or lower than the melting point of the resin formingthe first layer (1) and temperatures of the extrusion dies, the amountsof supplying the resins and the speed of moving the metal pipe and so onare controlled such that both layers are brought into contact with eachother and multiplexed.

Further, when the temperatures of the molten resins flowing out from thenozzle ports (11″) can pertinently be controlled, a single extrusioncoating device simultaneously extruding multiple layers of the firstlayer (1) and the second layer (2) can also be used.

After peeling off the second layer (2) at a pipe end portion of themetal pipe (P) formed with the multiple coat layer at its outerperipheral face in this way, a fastening nut for connection is insertedat the peeled-off portion, thereafter, end working is carried out andpredetermined bending is successively carried out.

EXAMPLES

Next, an explanation will be given of Examples according to the presentinvention along with Comparative Examples.

Example 1

A double-wound steel pipe formed into an outer diameter of 8 mm, a wallthickness of 0.7 mm and a length of 30 m is prepared by using a hoopmember having the material of SPCC on both faces of which copper platedlayers having a film thickness of 3 μm are constituted. A coated film ofZn having an average film thickness of 25 μm is formed on the outerperipheral face of the double-wound steel pipe by using an acidicelectrolyte having a major component of zinc sulfate and added with anorganic adding agent by conducting electricity for 2 minutes attemperatures of 55 through 60° C. and a current density of 60 A/dm².

Successively, after subjecting the surface of the Zn plated film tochromate treatment, the first layer is extruded to constitute a layerthickness of 50 μm by using the extrusion die (11₁) of the extrusioncoating device shown by FIG. 2 by using PA 12 as polyamide-based resinon the outer peripheral face of the steel pipe on which an epoxy-basedresin has been coated, heated and dried as a primer.

Further, polypropylene having no mutual dissolving performance inrespect with polyamide-based resin is extruded on the first layercomprising the polyamide-based resin layer to constitute a layerthickness of 1 mm by using the extrusion die (11₂) as shown by FIG. 2 bywhich the second layer is multiplexed with and coated on the firstlayer.

The obtained multiple coat metal pipe is cut into portions each having alength of 300 mm, the peel off test as shown by FIG. 1 is carried out inrespect of 6 pieces of samples among them by which it is found that thesecond layer is peeled off at a time point when parallel slits are cuttherein and the first layer does not adhere to the second layer at all.

Further, the obtained multiple coat metal pipe is cut into portions eachhaving a length of 200 mm, in respect of 6 pieces of samples among them,peeling off is carried out by a length of 100 mm or more, the peeled-offportions are cut into portions each having a length of 100 mm, both endportions thereof are masked, the peeled-off portions are dipped into ameasuring cylinder of 100 milliliter in which hydrochloric acid (1:1) isput by 100 milliliter and a depth of solution is 100 mm or more, andtaken out after a stationary state for 10 minutes and an amount ofdissolving of Zn is analyzed by an atomic absorption photometer. Aresult of the hydrochloric acid dipping test is shown by Table 1.

Example 2

After forming a Zn plated film similar to that in Example 1 on the outerperipheral face of a double-wound steel pipe formed similar to Example1, chromate treatment is carried out on the surface, silane couplingagent is coated successively, PA 11 is used as polyamide-based resin onthe outer peripheral face of the heated and dried steel pipe and thefirst layer is extruded to constitute a layer thickness of 30 m by aprocedure similar to that in Example 1.

Further, the second layer is multiplexed with and coated on the firstlayer by extruding polyethylene having no mutual dissolving performancein respect with polyamide-based resin on the first layer ofpolyamide-based resin to constitute a layer thickness of 1.5 μm by aprocedure similar to that in Example 1.

Similar to Example 1, the obtained multiple coat metal pipe is cut inportions each of 300 mm and with respect of 6 pieces of samples amongthem, the peel off test similar to that in Example 1 is carried out andas a result, in respect of each of the 6 pieces of samples, the secondlayer is peeled off at a time point when parallel slits are cut in thesecond layer and no adhesion is caused between the first layer and thesecond layer.

Further, similar to Example 1, with respect to 6 samples among samplescut into 200 mm, the hydrochloric acid-dipping test similar to that inExample 1 is carried out and a result of analysis is shown by Table 1.

Example 3

A Zn plated film is formed similar to Example 1 on the outer peripheralface of a double-wound steel pipe formed similar to Example 1.

Further, after carrying out chromate treatment on the surface of the Znplated film a first layer is extruded on the outer peripheral face ofthe steel pipe which has been coated with a titanium coupling agent,heated and dried to constitute a layer thickness of 40 μm by using PA 12having the melting point of 205° C. as polyamide-based resin.

Further, a second layer is multiplexed with and coated on the firstlayer by extrusion to constituted a layer thickness of 500 μm by usingPA 12 having the melting point of 165° C. as polyamide-based resinhaving mutual dissolving performance in respect with the first layer bya procedure similar to that in Example 1. Incidentally, temperature inextruding the second layer is 175° C. in the multiplexing and coatingoperation.

The obtained multiple coat metal pipe is cut into pieces each of 300 mmsimilar to Example 1, the peel off test similar to that in Example 1 iscarried in respect of 6 pieces of samples among them, by which it isfound that the peel off strength is 75 g/cm at maximum and in each of 6pieces of the samples, the first layer does not adhere to the secondlayer at all even when the second layer is peeled off.

Further, the hydrochloric acid-dipping test is carried out similar toExample 1 in respect of 6 pieces of samples among samples each cut to200 mm similar to Example 1 and the result of analysis is shown in Table1.

Example 4

A Zn plated film is formed similar to Example 1 on the outer peripheralface of a double-wound steel pipe formed similar to Example 1. Next,chromate treatment is carried out on the surface of the Zn plated filmand thereafter, a coating is carried out on the outer peripheral face ofthe steel pipe which has been coated with an epoxy-based resin as aprimer, heated and dried by dipping the steel pipe in a coating in whicha bisphenol type epoxy-based resin and pigment are prepared by asolvent, and the pipe is heated for 60 seconds by which an epoxy-basedresin layer having a film thickness of about 5 μm is formed.

Successively, a first layer is extruded on the outer peripheral face ofthe steel pipe formed with an epoxy-based resin similar to Example 1except that a layer thickness of 50 μm is constituted by using apolyvinylidene fluoride resin.

Further, a second layer is multiplexed with and coated on the firstlayer by extrusion to constitute a layer thickness of 1.0 mm by usingpolypropylene as a polyolefin resin by a procedure similar to that inExample 1.

The obtained multiple coat metal pipe is cut in pieces each of 300 mmsimilar to Example 1 and the peel off test similar to that in Example 1is carried out in respect of 6 pieces of samples among them by which itis found that with respect to each of 6 pieces of the samples, thesecond layer is immediately peeled off at a time point when parallelslits are cut therein and the first layer does not adhere to the secondlayer at all.

Further, the hydrochloric acid dipping test is carried out similar toExample 1 with respect to 6 pieces of samples among samples cut inpieces each of 200 mm similar to Example 1 and the result of analysis isshown by Table 1.

Comparative Example 1

A double-wound steel pipe is prepared and a Zn plated film is formed onits outer peripheral face similar to Example 1, successively, a coatingis carried out on the outer peripheral face of the steel pipe in whichchromate treatment has been carried out on the surface of the Zn platedfilm by dipping the steel pipe in a coating in which bisphenol typeepoxy-based resin and pigment are prepared by a solvent and the pipe isheated for 60 seconds at 300° C. by which an epoxy-based resin layerhaving a film thickness of about 15 μm is formed.

Successively, polyvinyl fluoride is coated on the steel pipe by dippingthe steel pipe in a solution in which polyvinyl fluoride is dispersed indiethyl phthalate, the pipe is dried by heating the pipe for 60 secondsat 350° C. by which a first layer is constituted by forming a polyvinylfluoride layer having a film thickness of about 15 μm.

Further, a thermally contractive tube comprising polyolefin resin andhaving a polyamide-based adhesive layer at an inner layer thereof isheated for 5 minutes at 160° C. thereby forming a second layer with alayer thickness of 1.0 mm.

The obtained multiple coat metal pipe is cut in pieces each of 300 mmsimilar to Example 1 and the peel off test similar to that in Example 1is carried out in respect of 6 pieces of samples among them by which itis found that the peel off strength is 3200 g/cm.

Further, the hydrochloric acid-dipping test is carried out similar toExample 1 with respect to 6 pieces of samples among samples each cut to200 mm similar to Example 1 and the result of analysis is shown by Table1.

Comparative Example 2

A double-wound steel pipe is prepared similar to Example 1, a Zn platedfilm is formed on the outer peripheral face similar to Example 1,chromate treatment is carried out on the surface of the Zn plated film,thereafter, multiple coating is carried out by extruding a first layerof a layer thickness of 50 μm comprising PA 12 having the melting pointof 165° C. on the outer peripheral face of the steel pipe in which anepoxy-based resin primer is coated, heated and dried and extruding asecond layer comprising PA 12 having the melting point of 205° C. in alayer thickness of 800 μm at an extrusion temperature of 250° C.

The obtained multiple coat metal pipe is cut in pieces each of 300 mmsimilar to Example 1 and the peel off test similar to Example 1 iscarried out with respect to 6 pieces of samples among them by which itis found that the peel off strength is 1240 g/cm at maximum and in eachof 6 pieces of samples, the first layer adheres to the second layer whenthe second layer is peeled off.

TABLE 1 Mutual dissolving Amount of performance dissolving Zn Example 1none 0 Example 2 none 0 Example 3 present 0 Example 4 none 0 ComparativeExample 1 none 7.32 Comparative Example 2 present Over 2000 (n = 6,unit: ppm)

Incidentally, in Table 1 described above, a value which is lower than aquantitative determination limit is set to 0.

According to a result of the peel off test and the hydrochloric aciddipping test in Table 1, it is found that in respect of the Examplesaccording to the present invention, corrosion resistance is achieved,the peel off operation in end working of flaring, spooling, buldging orthe like is facilitated since the peel off strength is weak and thecorrosion resistance at the end working portion is not deteriorated.Meanwhile, in Comparative Example 1, although the corrosion resistanceis achieved to some degree, the peel off operation is difficult and thecorrosion resistance of the peeled-off portion is deteriorated andaccording to Comparative Example 2, the corrosion resistance isdeteriorated, the peel off operation is difficult and the corrosionresistance of the end working portion is deteriorated.

Further, in respect of remaining 6 pieces provided by cutting each ofthe multiple coat metal pipes obtained by Examples 1 through 4 andComparative Examples 1 and 2 to 300 mm, soft chipping and hard chippingtests are carried out under the above-described conditions, the both endportions are masked, the samples are dipped into a measuring cylinder of100 milliliter constituting a depth of solution to 16 cm by puttinghydrochloric acid (1:1) by 100 milliliter, the samples are taken outafter a stationary state of 10 minutes and an amount of dissolving of Znis measured by an atomic absorption photometer by which it is found thatthe amount of dissolving of Zn in respect of each of the samples ofExamples 1 through 4 and Comparative Examples 1 and 2 is less than aquantitative determination limit and the soft chipping resistance andthe hard chipping resistance are achieved in the Examples according tothe present invention as well as the Comparative Examples.

As described above, according to the present invention, a multiple coatmetal pipe and its fabrication method having excellent corrosionresistance without deteriorating chipping resistance or splashingresistance, capable of being fabricated easily, capable of simplycarrying out peel off operation owing to a weak peel off strength wherecorrosion resistance of an end working portion is not deteriorated canbe provided.

What is claimed is:
 1. A multiple coat metal pipe which is a metal pipeconstituted by multiplexing and coating a first layer comprising a resinhaving an adhesive force in respect of a surface treatment layer formedon an outer peripheral face of the metal pipe and capable of beingextruded and a second layer provided on an outer perpheral face of thefirst layer, having a chipping resistance and capable of being extruded,wherein both the first layer and the second layer are substantially in anon-adhesive state such that a peel off strength between the first layerand the second layer is 75 g/cm or less whereby the peel off strengthenables the second layer to be peeled off from the first layer withoutdamaging the first layer.
 2. The multiple coat metal pipe according toclaim 1, wherein the metal pipe comprises any one of a seamless pipe, asemi-seamless pipe, an electrically welded pipe and either of a solderedpipe and a welded pipe having previously a film plated with a copperalloy and formed by being wound in a single layer or multiple layers. 3.The multiple coat metal pipe according to claim 1, wherein the surfacetreatment layer comprises a film plated with either of Zn, Al and alloyshaving base metals of these.
 4. The multiple coat metal pipe accordingto claim 3, wherein a chromate coating is coated further on a surface ofthe plated film.
 5. The multiple coat metal pipe according to claim 3 or4, wherein the surface treatment layer is coated with a primer selectedfrom the group consisting of single layers of epoxy resin, polyamideresin, a silane coupling agent and a titanium coupling agent.
 6. Themultiple coat metal pipe according to claim 1, wherein the first layercomprises polyamide resin and a layer thickness thereof is 20 through 50μm.
 7. The multiple coat metal pipe according to claim 1, wherein thesecond layer comprises a primer selected from the group consisting ofpolypropylene, polyethylene and a polyamide resin and a layer thicknessthereof is 100 μm through 1.5 mm.
 8. A method of fabricating a multiplecoat metal pipe, wherein a first layer comprising a resin having anadhesive force is extruded on a surface treatment layer provided on anouter peripheral face of a metal pipe and a second layer comprising aresin having a chipping resistance is extruded on an outer peripheralface of the first layer and the both resin layers are brought intocontact with each other and are multiplexed with each othersubstantially in a non-adhesive state such that a peel off strengthbetween the first layer and the second layer is 75 g/cm or less wherebythe peel off strength enables the second layer to be peeled off from thefirst layer without damaging the first layer.
 9. The method offabricating a multiple coat metal pipe according to claim 8, whereinwhen the first layer and the second layer are provided with mutualdissolving performance, the second layer is extruded at a temperatureequal to or lower than a melting point of the first layer.
 10. Themethod of fabricating a multiple coat metal pipe according to claim 8,where a surface treatment layer comprising a film plated with either ofZn, Al and alloys having base metals of these is formed on the outerperipheral face of the metal pipe.
 11. The method of fabricating amultiple coat metal pipe according to claim 10, chromate treatment iscarried out further on a surface of the plated film.
 12. The method offabricating a multiple coat metal pipe according to claim 10 or 11,wherein the surface treatment layer is further coated with a primerselected from the group consisting of single layers of expoxy resin,polyamide resin, a silane coupling agent and a titanium coupling agentas a primer by a method of either of extrusion forming, spraying,showering, dipping, bush coating, powder coating and hot melting. 13.The method of fabricating a multiple coat metal pipe according to claim8, wherein the first layer compromising a polyamide resin is extruded toa layer thickness of 20 through 50 μm.
 14. The method of fabricating amultiple coat metal pipe according to claim 8, wherein the second layercomprising a primer selected from the group consisting of polypropylene,polyethylene and a polyamide resin is extruded to constitute a layerthickness of 100 μm through 1.5 mm.
 15. The method of fabricating amultiple coat metal pipe according to claim 13 or 14, wherein thepolyamide resin comprises either of PA 6, PA 11 and PA 12.